System and method for providing stable control for power systems

ABSTRACT

System and method for providing stable control for power systems. According to an embodiment, the present invention provides an apparatus for providing one or more control signals for a power system. The apparatus includes an input terminal for receiving an electrical energy, which can be characterized by a first input voltage. The apparatus includes a control component that is configured to generate a first control signal based on at least information associated with the first input voltage. The apparatus additionally includes an output terminal for sending the first control signal. Moreover, the apparatus includes a timing component that is coupled to the control component. The control component is configured to process at least information associated with a first value of the first input voltage at a first time and a first reference voltage and to generate a second control signal.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/692,098, filed Mar. 27, 2007, which claims priority to Chinese Patent Application No. 200710038167.7, filed Mar. 24, 2007, entitled “SYSTEM AND METHOD FOR PROVIDING STABLE CONTROL FOR POWER SYSTEMS”, by inventors Yuan Lin, Jun Ye, and Lieyi Fang, both applications being commonly assigned and incorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

The present invention is related to integrated circuits. More specifically, the present invention can be applied to devices used controlling power supply. According to various embodiments, the present invention provides various power control schemes to improve system stability and performance. Merely by way of example, the present invention can be used in switch mode power conversion system including power-on reset and under voltage lockout circuits. It is to be appreciated that the present invention has a broad range of applications.

Power converters are widely used in various applications, such as providing power to portable consumer electronics. The power converters can convert electric power from one form to another form. As an example, the electric power is transformed from alternate current (AC) to direct current (DC), from DC to AC, from AC to AC, or from DC to DC. Additionally, the power converters can convert electric power from one voltage level to another voltage level. By converting electrical power to desired form and/or voltage, various devices can be properly powered.

In the past various types of power converters have been developed. For example, linear regulators have traditionally been used for power converters. A linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its “linear region” or passive devices like zener diodes operated in their breakdown region. The regulating device is made to act like a variable resistor. While linear regulators have been used for many years, their power efficiency is often inadequate for portable electronics. For example, due to low power efficiency, linear regulators often waste large amount of energy and generate excessive heat for portable devices.

With the advent of integrated circuits, switched-mode power supply has been invented and utilized for various applications. Switch mode power supplies are typically implemented with a switching regulator, which is an internal control circuit that switches the load current rapidly on and off in order to stabilize the output voltage. For certain applications, switch-mode power supply uses pulse-width-modulated (PWM) or pulse-frequency-modulated (PFM) mechanism. These mechanisms are usually implemented with a switch-mode-controller including various protection components.

Typically, various types of power supplies are controlled by power-on reset (POR) and under voltage lockout (UVLO) circuits. For example, POR/UVLO circuits are used to hold the electronic systems in a “reset” mode during power on and off transitions. In addition, POR and UVLO circuits are sometimes used when the power supply voltage, which typically ranges from several volts to several tens of volts, is in an invalid state.

When an integrated circuit initializes (e.g., when powering up), the process usually starts with the supply voltage of the integrated circuit being switched on. During this process, the supply voltage will rise from zero to an operational supply voltage within a certain amount source impedance or source current. Before the operational supply voltage is reached, the integrated circuit is unable to properly function. Typically, the integrated circuit at this voltage is in an undefined and/or invalid state. For example, when the integrated circuit is at an undefined state, the integrated circuit should not operate; operating in an undefined state could potentially cause damages to the integrated circuit.

As explained above, it is thus desirable to prevent the integrated circuit from operating when it is in an undefined and/or invalid state (e.g., due to insufficient supply voltage). To disable integrated circuit form operating in an undefined state, the integrated circuit is usually put in to a reset mode, which can be accomplished by an UVLO circuit.

In addition to preventing the integrated circuit from operating when it is in an undefined and/or invalid state, it is often desirable to assure that various components of the integrated circuit are in a properly initialized before the integrated circuit starts fully operating. Usually, a POR/UVLO circuit is used to monitor voltages at various nodes of the integrated circuits to determine whether various components are properly initialized (e.g., whether these components reached their threshold voltage levels). Based on the monitored voltages, the POR/UVLO generates control signals that enable and/or disable various components and/or the integrated circuit.

Over the past, POR/UVLO circuits have widely used for various power systems. Conventional techniques for POR/UVLO power control have been developed to make POR/UVLO circuits more efficient and reliable. Unfortunately, these conventional techniques are often inadequate.

Therefore, it is desirable to have improved systems and methods for power control systems.

BRIEF SUMMARY OF THE INVENTION

The present invention is related to integrated circuits. More specifically, the present invention can be applied to devices used controlling power supply. According to various embodiments, the present invention provides various power control schemes to improve system stability and performance. Merely by way of example, the present invention can be used in switch mode power conversion system including power-on reset and under voltage lockout circuits. It is to be appreciated that the present invention has a broad range of applications.

In certain embodiments, the present invention is implemented with power on-reset (POR) and under voltage lock out (UVLO) circuit. For example, certain POR/UVLO circuits according to present invention are used as parts of switched power conversion controllers, which can be used to initialize integrated pulse width modulation (PWM) circuits. In a specific embodiment, a POR/UVLO circuit according to the present invention utilizes a timing device to prevent undesirable toggling of control signals, which often occurs when the a power system in operating in light-to-heavy load transition.

According to an embodiment, the present invention provides an apparatus for providing one or more control signals for a power system. The apparatus includes an input terminal for receiving an electrical energy, which can be characterized by a first input voltage. The apparatus also includes a control component that is configured to generate a first control signal based on at least information associated with the first input voltage. The apparatus additionally includes an output terminal for sending the first control signal. Moreover, the apparatus includes a timing component that is coupled to the control component. The control component is further configured to process at least information associated with a first value of the first input voltage at a first time and a first reference voltage and to generate a second control signal based on at least information associated with the first voltage and the first reference voltage. The timing component is configured to receive the second control signal and in response to the second control signal to generate a third control signal after a period of time delay. The control component is further configured to receive the third control signal and, in response to the third control signal, process information associated with a second value of the first input voltage at a second time and the first reference voltage and to generate the first control signal based on at least information associated with the first voltage and the first reference voltage. The first control signal is capable to cause one or more components of the power system to be turned off.

According to another embodiment, the present invention provides an apparatus for providing one or more control signals for a power system. The apparatus includes an input terminal for receiving electrical energy, which is characterized by a first voltage. The apparatus also includes a control component that is configured to generate a control signal based on the first voltage. The control signal is capable to cause one or more components of the power system to be turned on or off. The control component is further configured to compare the first voltage to a first reference voltage and a second reference voltage. The first reference voltage is lower than the second reference voltage. The apparatus additionally includes an output terminal for sending the control signal. Moreover the apparatus includes a timer that is configured to provided a delay time. The control component generates an on signal if the first voltage rises above the second reference voltage. The timer initiates if the first voltage drops below the first reference voltage at a first time. The control component generates an off signal if the first voltage is below the first reference voltage at a second time. For example, the second time is elapse of delay time after the first time.

According to yet another embodiment, the present invention provides a method for providing one or more control signals for a power system. The method includes a step for providing a first reference voltage and a second reference voltage. The first reference voltage is lower than the second reference voltage. The method also includes a step for determining a voltage that is associated with a load condition of the power system. The method further includes a step for providing a first signal if the voltage rises above the second reference voltage. The first signal is capable of causing one or more components of the power system to be turned on. The method also includes a step for initiating a timer if the voltage drops below the first reference voltage at a first time. Moreover, the method includes a step for providing a second signal if the voltage is below the first reference voltage at a second time. The second time is later than the first time by a predetermined amount of time. For example, the second signal is capable of causing the one or more components of the power system to be turn off.

According to yet another embodiment, the present invention provides a method for providing one or more control signals for a power system. The method includes a step for receiving an electrical energy that is characterized by a first input voltage. The method also includes a step for providing a first reference voltage and a second reference voltage. The method additionally includes a step for processing at least information associated with a first value of the first input voltage at a first time and a first reference voltage by a control component. As an example, the control component is configured to generate a first control signal. The method additionally includes a step for generating a second control signal based on at least information associated with the first voltage and the first reference voltage. Moreover, the method includes a step for sending the second control signal to a timing component. Furthermore, the method includes a step for sending a third control signal to the control component by the timing component after a period of time delay. Additionally, the method includes a step for processing information associated with a second value of the first input voltage at a second time and the first reference voltage by the control component. Also, the method includes a step for generating the first control signal based on at least information associated with the first voltage and the first reference voltage. The first control signal is capable to cause one or more components of the power system to be turned off.

It is to be appreciated that the present invention provides various advantages over conventional techniques. According to an embodiment, the present invention provides a more energy efficient solution as compared to conventional techniques. For example, the present invention reduces the numbers of transitions between on and off states of a power supply. More specifically, embodiments of the present invention reduces the number of undesirable transition between on and off due to glitches in the power system. According to certain embodiment, the present invention offers a large window for power control and great flexibility. For example, more than one threshold voltage threshold values are used in determining various states of the power supply. In addition, it is to be appreciated that various embodiments of the present invention are compatible and easily implemented with conventional systems. There are other benefits as well.

Various additional objects, features and advantages of the present invention can be more fully appreciated with reference to the detailed description and the accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating a conventional power system.

FIG. 2 is a simplified diagram illustrating a conventional POR/UVLO circuit as used in a power system.

FIG. 3 is a simplified timing diagram illustrating the operation of a POR/UVLO circuit.

FIG. 4 is a simplified timing diagram illustrating operation of conventional POR/UVLO circuits.

FIG. 5 is a simplified diagram illustrating a POR/UVLO circuit according to an embodiment of the present invention

FIG. 6 is a simplified flow diagram illustrating operation of a power control component according to an embodiment of the present invention.

FIG. 7 is a simplified diagram illustrating a control system according to an embodiment of the present invention.

FIG. 8 is a simplified timing diagram illustrating the operation of a control system according to an embodiment of the present invention

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to integrated circuits. More specifically, the present invention can be applied to devices used controlling power supply. According to various embodiments, the present invention provides various power control schemes to improve system stability and performance. Merely by way of example, the present invention can be used in switch mode power conversion system including power-on reset and under voltage lockout circuits. It is to be appreciated that the present invention has a broad range of applications.

As described above, power-on reset (POR) and under voltage lockout (UVLO) circuits are widely used for power systems. Typically, characteristics of operation of POR/UVLO circuits are related to various parameters (e.g., impedance level, power input, etc.).

FIG. 1 is a simplified diagram illustrating a conventional power system. A conventional power system 100 includes an AC power supply 102, which is rectified by the rectifier 103, and the supplied to a PWM controller circuit 110 through a resistor 101 (i.e., often referred to as startup resistor). The resistor 101 is a necessary for starting a PWM signal generator 112. At the same time, the resistor 101 is often a source of significant energy inefficient during the operation of the PWM signal generator 112, as the resistor 101 is typically characterized by large impedance value (up to several mega ohms). For example, between the two terminals of the resistor 101, difference in voltage potential between node 106 and node 107 is great. As an example, the voltage at node 106 can be at 370 volts DC while the VDD voltage at the node 107 is as low as 12 volts DC. Thus, the large voltage drop due to the resistor 101 during the continuous operation of the power system leads to significant energy loss, especially when the power system 100 is operating in light or no load conditions. In addition to energy inefficiency, the large value of the resistor 101 also leads to low source current (e.g., as low as several tens of micro amps) supplied to the PWM generator 112. It is therefore desirable to have a POR/UVLO circuit with low quiescent current consumption.

FIG. 2 is a simplified diagram illustrating a conventional POR/UVLO circuit as used in a power system. A POR/UVLO circuit 200 turns on or off based its input voltage and reference voltages UVLO(OFF) and UVLO(ON). For example, a hysteresis voltage between UVLO(OFF) and UVLO(ON) prevents the supply voltage VDD (e.g., voltage at node 107 in FIG. 1) from being unstable during power on/off sequences. As an example, during a startup process, the power system is turned on when the capacitor 120 (as shown in FIG. 1) is charged up to UVLO(OFF) voltage level through the resistor 101 (as shown in FIG. 1).

During, the output 201 of the POR/UVLO circuit 200 is controlled by the switches 202 and 203. For example, when the VDD voltage ramps up to UVLO(OFF) at node 204, both switches are turned on, and as a result the POR output 205 changes from zero to one. As an example, when the VDD voltage drops (e.g., during a process of powering off), the switches 202 and 203 are turned off, which causes the POR output 204 to change from “1” to “0”.

In certain applications, the output 201 of the POR/UVLO circuit 200 can be used to control a high-to-low voltage regulator (e.g., a part of the interval low voltage components). For example, when the voltage at node 204 drops below threshold voltage UVLO(ON), the POR output 204 is low, which disables the high-to-low regulator.

The POR output 204 depends on the VDD voltage, the UVLO(ON) voltage, and the UVLO(OFF) voltage. Based on the diagram as shown in FIG. 2, the UVLO(ON) voltage may be expressed by the following equation. UVLO(ON)=V _(th) _(—) _(M1) +V _(DZ2) +V _(D1)  (Equation 1)

In Equation 1, the V_(th) _(—) _(M1) voltage represents the voltage of the switch 202, the V_(DZ2) represents the voltage of the diode 213, and the term V_(D1) represents the voltage of the diode 212.

Similarly, the UVLO(OFF) voltage may be expressed by the following equation. UVLO(OFF)=V _(th) _(—) _(M1) +V _(DZ2) +V _(D1) +V _(DZ1)  (Equation 2)

In Equation 2, the V_(th) _(—) _(M1) voltage represents the voltage of the switch 202, the V_(DZ2) represents the voltage of the diode 213, the term V_(D1) represents the voltage of the diode 212, and the term V_(DZ1) represents the voltage of the diode 211.

FIG. 3 is a simplified timing diagram illustrating the operation of a POR/UVLO circuit. As shown in FIG. 3, the POR output changes from zero to one when the VDDH voltage rises above the UVLO(OFF) voltage; the POR voltage changes from one to zero when the VDDH voltages drops below the UVLO(ON) voltage.

A conventional POR/UVLO circuit as shown in FIG. 2 is effective in preventing a power system from damages under various conditions. Unfortunately, such conventional POR/UVLO circuit is often inefficient and unstable. For example, a temporary supply voltage fluctuation of the power system could lead the POR/UVLO circuit to send a reset signal to the power system, causing the power system to shut down and restart. As an example, sudden temporary drop in supply voltage occurs when the power system experiences a transition of system load from light to heavy.

Typically, when load of the power system is light, the supply voltage (i.e., VDD voltage) is close to UVLO(ON). When load on the power system increases abruptly, the supply voltage usually drops temporarily. Typically, the voltage drop of the supply voltage is due to finite loop bandwidth and transformer coupling (e.g., see couple 140 in FIG. 1) between a secondary side and auxiliary side, which provides energy to PWM controller (e.g., PWM controller 110 in FIG. 1). Usually, the heavier is the loading transition, the larger is the supply voltage drop. In certain occasions, when the loading transition is heavy enough, the supply voltage would drop below the UVLO(ON) voltage, causing system to restart.

FIG. 4 is a simplified timing diagram illustrating operation of conventional POR/UVLO circuits. As seen in FIG. 4, abrupt loading changes could result in undesired UVLO process. For example, the loading is suddenly increased at t₁. The VDD voltage level, due to the sudden increase of the load, drops drastically at t₁. At t₂, the VDD voltage level drops below the threshold voltage level UVLO(ON), causing the POR/UVLO circuit to stop PWM switching at t₂. The drop in VDD voltage level, however, is only temporary. As shown, the power supply steadily ramps up the VDD voltage at t₂ in response to the loading increase. At t₃, the VDD voltage is increased to a voltage level that is higher than the threshold voltage level UVLO(OFF), causing the POR/UVLO circuit to restart PWM switching.

While the POR/UVLO circuits are designed to protect a power system from being damaged from sudden change in operational parameters in a power circuit, shutting down the PWM switching for the abovementioned scenario is generally undesirable. For example, the drop of the VDD voltage is only temporary, and thus shutting down the PWM switching is unnecessary and undesirable. For example, between t₂ and t₃, the PWM switching remains off despite the fact that the VDD voltage is not low enough to warrant turning off of PWM switching. In addition, undesired shutting off of PWM switching renders the power system less stable and subject to restarts caused by minor glitches.

It is to be appreciated that certain embodiments of the present embodiments provide stable and efficient method and system for controlling power system. For example, a specific embodiment of the present invention involves a technique for improving system stability of a power system by reducing and/or eliminating undesirable shutting off the system.

In a specific embodiment, the present invention provides a POR/UVLO circuit that includes a mechanism for reducing and/or eliminating undesirable shutting off of the system. FIG. 5 is a simplified diagram illustrating a POR/UVLO circuit according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.

As shown in FIG. 5, a control system 500 includes, but not limited to, the following components:

1. a voltage input;

2. a voltage sensor 502;

3. a voltage regulator 503;

4. a voltage comparator 553;

5. a reference voltage 554;

6. a timer 552;

7. switches 512,513, and 514; and

8. an AVDD component 550.

The control system 500 is capable of, like conventional POR/UVLO circuits, causes various components of a power system to be turned on or off based on one or more input voltages. As shown in Figure 5, the control system 500 includes a POR/UVLO circuit 510. The POR/UVLO circuit 510 is a part of the control system 500 and includes the voltage input, switches 512, 513, and 514, and a POR output 590. Now referring back to the control system 500, which includes the timer 552 that is connected to the comparator 553. For example, the timer 552 is a delay timer that delays the output of the comparator 553 before the output is supplied to the POR/UVLO circuit 510 for the determination of whether a power off signal is to be sent. Depending upon application, the timer 552 may be implemented in various ways. Merely by way of example, the timer 552 may be implemented by an RC filter, which timing characteristics are based on the values of resistors and capacitors. Also, the timer 552 may be implemented with other means, such as latches, oscillators, etc.

In a specific embodiment, the present invention implements the timer 552 using a timer circuit. It is to be appreciated that the timer circuit occupies less chip area and is able to generate time delays characterized by different properties as compared to an RC timer. For example, a timer circuit according to a specific embodiment of the invention is implemented within a small chip area.

As shown in FIG. 5, the POR/UVLO circuit 510 can be characterized by a latch structure and two threshold voltages: UVLO(OFF) and UVLO(ON) threshold voltages. The POR/UVLO circuit 500 has a voltage input, which is electrically coupled to a power supply at a terminal VDDH 504. For example, the UVLO(OFF) voltage is associated with the voltage at the terminal VDDH 504. Depending upon application, the POR/UVLO circuit 510 may receive other signal inputs. For example, a different input signal is used to control the UVLO(ON) voltage. The POR output 590 is supplied to the voltage regulator 503, which in turn provides low voltage supply signal to the AVDD component 550. In addition the low voltage supply signal, the AVDD component 550 also receives a signal from the VDDH sensor 502. For example, the VDDH sensor 502 provides a scaled VDDH signal based on specific applications.

The VDDH sensor 502 may be implemented in various ways. For example, the VDDH sensor is implemented by a resistor divider, which can be combined with the POR/UVLO circuit 510. The scaled VDDH signal from the VDDH sensor 502 is provided to the comparator 553 of the AVDD component. In addition to the scaled VDDH signal from the VDDH sensor 502, the comparator also receives a reference voltage from the reference voltage input 554. As an example, the reference voltage may be adjusted according to specific application.

The comparator 553 compares the reference voltage and the scaled VDDH signal and generates a comparator output signal to the timer 552. Among other things, the timer 552 is able to debounce the comparator output signal for a predetermined time. For example, if the scaled VDDH signal is lower than the reference voltage for the predetermined time, the output of the timer 552 causes the POR/UVLO circuit 510 to change state, thereby changes the POR output 590 from one to zero. On the other hand, if the scaled VDDH signal is lower than the reference voltage for less the predetermined time, the output of the timer 552 does not cause the POR/UVLO circuit 510 to change state. It is to be appreciated that based on specific applications, the predetermined time may be adjusted. Typically, the predetermined time is long enough to prevent undesired shutting down of the system due to temporary system glitch yet is not too long to hinder the proper functioning of the power system.

It is to be appreciated that the control system 500 may be implemented to adaptable for implementation with conventional power systems. For example, the control system 500 is implemented in conjunction with the power system 100 as illustrated in FIG. 1.

To further illustrate the operation of the present invention, a flow diagram is presented. FIG. 6 is a simplified flow diagram illustrating operation of a power control component according to an embodiment of the present invention. This diagram is merely an example, which could be altered and modified, and should not unduly limit the scope of claims. For example, various steps as illustrated in FIG. 6 may be added, removed, replaced, rearranged, repeated, overlapped, and/or partially overlapped. Merely by way of an example, a flow diagram 600 illustrates the operation of the control system 500 that is used to provide control for a power system. For example, the power system is similar to the power system 100 in various ways.

At step 601, the power system is set to a start up state. Typically, before the power system receives power input from one or more power supply, various components should be turned off to prevent these components from being damaged. For example, the control system 500 sends a signal indicating that POR=0, which consequently causes various components (e.g., PWM switching component, etc.) to be turned off.

At step 602, the power system is turned on. According to various embodiments, the power system is turned on when a power supply that is connected to the power system is turned on. To ensure the proper functioning of power system and components thereof, the power system does not turn on all its components before it is determined that the power level at the power system is stable and operations. For example, before the power from power supply is provided to the PWM switching component of the power system, the control system 500 determines whether the power system and power system are in working order.

At step 603, the control system determines whether the supply voltage has reached an operational threshold. According to an embodiment, the control system compares the VDD supply voltage against a predetermined threshold voltage level UVLO(OFF). If the VDD supply voltage is greater than the UVLO(OFF) voltage, the control system proceeds to step 604. As explained above, the UVLO(OFF) voltage is a threshold voltage that indicates whether the supply voltage is sufficient enough to allow the power system to properly operate. Depending upon application, the UVLO(OFF) voltage may be modified based on the specific needs. On the other hand, if the VDD supply voltage is less than the UVLO(OFF) voltage, the control system repeats step 603 after a predetermined time period.

At step 604, the control system generates a signal to turn on the power system. In a specific application, the control system provides a signal indicating POR=1, enabling PWM switching of the power system, thus turning on various components of the power system.

At step 605, the control system determines whether the supply voltage has dropped below a threshold voltage. In an embodiment, the threshold voltage is UVLO(ON) voltage. Merely by way of an example, the control system constantly monitors the supply voltage level in real time. If the VDD supply voltage is less than the UVLO(ON) voltage, the control system proceeds to step 605. As explained above, the UVLO(ON) voltage is a threshold voltage that indicates whether the supply voltage is too low to warrant the power system being turned off. Depending upon application, the UVLO(ON) voltage may be modified based on the specific needs. On the other hand, if the VDD supply voltage is greater than the UVLO(ON) voltage, the control system proceeds to step 604 after a predetermined time period.

At step 606, the control system determines whether the supply voltage is below the UVLO(ON) threshold after an elapse of a predetermined time. For example, the timer 552 in FIG. 5 causes the control system to wait for the predetermined time before the control system sends control signals for turning the power system off. In a specific embodiment, after the predetermined time, the control system compares the supply voltage with the UVLO(ON) voltage. If the VDD supply voltage is less than the UVLO(ON) voltage, the control system proceeds to step 601 (i.e., turning off and resetting the power system). On the other hand, if the VDD supply voltage is greater than the UVLO(ON) voltage, the control system proceeds to step 604.

FIG. 7 is a simplified diagram illustrating a control system according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.

As shown in FIG. 7, a control system 700 includes, among other things, the following components:

1. zener diodes 701 and 703;

2. a diode 702;

3. resistors 705, 706, 708, and 715;

4. switches 704, 707, and 709;

5. an inverter 710;

6. a voltage regulator 711;

7. a reference voltage 714;

8. a comparator 713; and

9. a timer 712.

As an example, the control system 700 operates in essentially the same way as the control system 500. According to certain embodiments, the control system 700 is compatible with conventional power systems (e.g., the power system 100 in FIG. 1). It is to be appreciated that the control system 700 may be flexibility implemented using various types of components. For example, switches 704, 707, and 709 is implemented using MOSFETs in certain applications, but can be implemented using other types of devices as well (e.g., BJT, etc.). Similarly, the timer 712 may be implemented with various types of devise as well, which is explained above. For example, the timer 712 is implemented using low-voltage device, as relatively long period of delay time may be achieved using frequency divided PWM clock.

The control system 700 generates control signals, which are produced from switches. The output of POR output 750 is triggered by the switch 707. For example, the switch 707 is implemented with a high voltage NMOS in conjunction with resistor 708 and a voltage divider. Merely by way of example, the voltage divider is implemented using resistors 705 and 706 connected in series, which is for sensing the VDDH voltage.

The voltage level determination is performed by the voltage comparator 713. In some embodiments, the voltage comparator 713 is a low voltage comparator. The Voltage comparator 713 is connected to the reference voltage 714 to determine whether the supply voltage VDD is above one or more threshold voltages. As an example, the output of the voltage comparator 713 is delayed by the timer 712, which uses an internal oscillator clock of the PWM controller as one of its input.

The operation of the control system 700 may be illustrated the followings. When the power is turned on for the system, the control system 700 provides the POR signal without delay by the timer 712. For example, when the power system turns on, before the POR signal switches from zero to one, the voltage regulator is at a disabled state. As a result, no power is available to various components of the control system. For example, when no power is available various components (e.g., switch 707) may be in undefined states. The resistor 708 is used to eliminate undefined states of these components, and thus the switch 707 is not triggered when the voltage regulator 711 is not ready.

When the power system powers off, the supply voltage VDDH ramps down. At certain point, the supply voltage VDDH drops below a predetermined voltage UVLO(ON). When this happens, the timer 712 is triggered to delay the comparator output for a predetermined time. When the predetermined time, the output of the comparator 713 is passed through the timer 712 to the switch 707, which turns on or off switches 704 and 709. If the predetermined time is not yet over, the output of the comparator 713 cannot passed through the timer 712. During the operation, the resistor 708 functions as a pull down resistor that is used to ensure proper operation of the switches after the power system is on.

According to certain implementation of the control system 700, two UVLO(ON) voltages are used. For example, a UVLO(ON) voltage is in accordance with functions of the timer 715 while a UVLO(ON)_H voltage functions in essentially the same way as a conventional UVLO(ON) threshold voltage. For example, the UVLO(ON) voltage is associated with the timer 712. For the two UVLO(ON) voltage thresholds to properly function in conjunction with the timer 712, the UVLO(ON) threshold voltage is higher than the UVLO(ON)_H threshold voltage, and the control system 700 generates control signals based on the UVLO(ON) threshold voltage. As an example, the relationships among threshold voltages are illustrated according to the following equations.

$\begin{matrix} {{{UVLO}({ON})} = {{V_{th} \cdot \left( {1 + \frac{R_{1}}{R_{2}}} \right)} + V_{{DZ}\; 2} + V_{D\; 1}}} & \left( {{Equation}\mspace{14mu} 3} \right) \\ {{{{UVLO}({ON})}{\_ H}} = {V_{{th\_ M}\; 2} + V_{{DZ}\; 2} + V_{D\; 1}}} & \left( {{Equation}\mspace{14mu} 4} \right) \\ {{{UVLO}({ON})} \geq {{{UVLO}({ON})}{\_ H}}} & \left( {{Equation}\mspace{14mu} 5} \right) \end{matrix}$

FIG. 8 is a simplified timing diagram illustrating the operation of a control system according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown in FIG. 8, the control system 700 changes the POR output from zero to one when VDDH ramps up above the threshold voltage UVLO(OFF) at t1. When the VDDH voltage drops below UVLO(ON) at t2, the control system changes the POR output from one to zero. As explained above, the UVLO(ON) voltage referred here is different from the UVLO(ON) voltage used in a conventional power system. For example, the UVLO(ON) voltage according to the embodiments of the present invention is higher than the UVLO(ON) voltage of conventional power systems.

According to an embodiment, the present invention provides an apparatus for providing one or more control signals for a power system. The apparatus includes an input terminal for receiving an electrical energy, which can be characterized by a first input voltage. The apparatus also includes a control component that is configured to generate a first control signal based on at least information associated with the first input voltage. The apparatus additionally includes an output terminal for sending the first control signal. Moreover, the apparatus includes a timing component that is coupled to the control component. The control component is further configured to process at least information associated with a first value of the first input voltage at a first time and a first reference voltage and to generate a second control signal based on at least information associated with the first voltage and the first reference voltage. The timing component is configured to receive the second control signal and in response to the second control signal to generate a third control signal after a period of time delay. The control component is further configured to receive the third control signal and, in response to the third control signal, process information associated with a second value of the first input voltage at a second time and the first reference voltage and to generate the first control signal based on at least information associated with the first voltage and the first reference voltage. The first control signal is capable to cause one or more components of the power system to be turned off. As an example, the embodiment is illustrated according to FIG. 7.

According to another embodiment, the present invention provides an apparatus for providing one or more control signals for a power system. The apparatus includes an input terminal for receiving electrical energy, which is characterized by a first voltage. The apparatus also includes a control component that is configured to generate a control signal based on the first voltage. The control signal is capable to cause one or more components of the power system to be turned on or off. The control component is further configured to compare the first voltage to a first reference voltage and a second reference voltage. The first reference voltage is lower than the second reference voltage. The apparatus additionally includes an output terminal for sending the control signal. Moreover the apparatus includes a timer that is configured to provided a delay time. The control component generates an on signal if the first voltage rises above the second reference voltage. The timer initiates if the first voltage drops below the first reference voltage at a first time. The control component generates an off signal if the first voltage is below the first reference voltage at a second time. For example, the second time is elapse of delay time after the first time. As an example, the embodiment is illustrated according to FIG. 7.

According to yet another embodiment, the present invention provides a method for providing one or more control signals for a power system. The method includes a step for providing a first reference voltage and a second reference voltage. The first reference voltage is lower than the second reference voltage. The method also includes a step for determining a voltage that is associated with a load condition of the power system. The method further includes a step for providing a first signal if the voltage rises above the second reference voltage. The first signal is capable of causing one or more components of the power system to be turned on. The method also includes a step for initiating a timer if the voltage drops below the first reference voltage at a first time. Moreover, the method includes a step for providing a second signal if the voltage is below the first reference voltage at a second time. The second time is later than the first time by a predetermined amount of time. For example, the second signal is capable of causing the one or more components of the power system to be turn off. As an example, the embodiment is illustrated according to FIG. 6.

According to yet another embodiment, the present invention provides a method for providing one or more control signals for a power system. The method includes a step for receiving an electrical energy that is characterized by a first input voltage. The method also includes a step for providing a first reference voltage and a second reference voltage. The method additionally includes a step for processing at least information associated with a first value of the first input voltage at a first time and a first reference voltage by a control component. As an example, the control component is configured to generate a first control signal. The method additionally includes a step for generating a second control signal based on at least information associated with the first voltage and the first reference voltage. Moreover, the method includes a step for sending the second control signal to a timing component. Furthermore, the method includes a step for sending a third control signal to the control component by the timing component after a period of time delay. Additionally, the method includes a step for processing information associated with a second value of the first input voltage at a second time and the first reference voltage by the control component. Also, the method includes a step for generating the first control signal based on at least information associated with the first voltage and the first reference voltage. The first control signal is capable to cause one or more components of the power system to be turned off. As an example, the embodiment is illustrated according to FIG. 6.

It is to be appreciated that the present invention provides various advantages over conventional techniques. According to an embodiment, the present invention provides a more energy efficient solution as compared to conventional techniques. For example, the present invention reduces the numbers of transitions between on and off states of a power supply. More specifically, embodiments of the present invention reduces the number of undesirable transition between on and off due to glitches in the power system. According to certain embodiment, the present invention offers a large window for power control and great flexibility. For example, more than one threshold voltage threshold values are used in determining various states of the power supply. In addition, it is to be appreciated that various embodiments of the present invention are compatible and easily implemented with conventional systems. There are other benefits as well.

Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims. 

1. A controller for a power system, the controller comprising: a first resistor including a first resistor terminal and a second resistor terminal, the first resistor terminal configured to receive a first voltage signal, the second resistor terminal being connected to a first circuit node; a first transistor including a first transistor terminal, a second transistor terminal, and a third transistor terminal, the first transistor terminal being configured to receive a second voltage signal from the first circuit node, the second transistor terminal being configured to receive a third voltage signal from a second circuit node, the third transistor terminal being connected to a third circuit node; a second resistor including a third resistor terminal and a fourth resistor terminal, the third resistor terminal being connected to the second circuit node; a third resistor including a fifth resistor terminal and a sixth resistor terminal, the fifth resistor terminal being connected to the fourth resistor terminal through a fourth circuit node, the sixth resistor terminal being connected to the third circuit node; a second transistor including a fourth transistor terminal, a fifth transistor terminal, and a sixth transistor terminal, the fourth transistor terminal being connected to the second circuit node, the sixth transistor terminal being connected to the third circuit node; a voltage regulator configured to receive at least the first voltage signal and to convert the first voltage signal to a fourth voltage signal, the fourth voltage signal being smaller than the first voltage signal in magnitude; a threshold voltage generator configured to receive the fourth voltage signal and to generate a threshold voltage signal; a voltage comparator configured to receive the threshold voltage signal and a fifth voltage signal from the fourth circuit node, compare the threshold voltage signal and the fifth voltage signal, and to generate a comparison signal; and a timer configured to receive the comparison signal, provide a delay time, and output a sixth voltage signal.
 2. The controller of claim 1 is further configured: to determine whether the fifth voltage signal is below the threshold voltage signal in magnitude at a first time; if the fifth voltage signal is determined to be below the threshold voltage signal in magnitude at the first time, to determine again whether the fifth voltage signal is below the threshold voltage signal in magnitude at a second time, the second time being later than the first time by the delay time; and if the fifth voltage signal is determined to be below the threshold voltage signal in magnitude at the first time and if the fifth voltage signal is also determined to be below the threshold voltage signal in magnitude at the second time, to provide an off signal as the power-on-reset signal to at least the voltage regulator.
 3. The controller of claim 2 is further configured, if the fifth voltage signal is determined to be below the threshold voltage signal in magnitude at the first time and if the fifth voltage signal is determined not to be below the threshold voltage signal in magnitude at the second time, not to provide the off signal.
 4. The controller of claim 1, and further comprising a fourth resistor including a seventh resistor terminal and an eighth resistor terminal, the seventh resistor terminal being connected to the fifth transistor terminal, the eighth resistor terminal being connected to the third circuit node.
 5. The controller of claim 1 wherein the timer includes an RC filter.
 6. The controller of claim 1 wherein the timer includes a latch.
 7. The controller of claim 1, and further comprising an oscillator configured to output a clock signal to the timer.
 8. The controller of claim 1 wherein the delay time is predetermined.
 9. The controller of claim 1, and further comprising: a first zener diode including a first diode terminal and a second diode terminal, the first diode terminal configured to receive the first voltage signal; a third transistor including a seventh transistor terminal, an eighth transistor terminal, and a ninth transistor terminal, the seventh transistor terminal configured to receive the first voltage signal, the eighth transistor terminal being connected to the first circuit node, the ninth transistor terminal being connected to the second diode terminal; a first diode including a third diode terminal and a fourth diode terminal, the third diode terminal being connected to the second diode terminal; and a second zener diode including a fifth diode terminal and a sixth diode terminal, the fifth diode terminal being connected to the fourth diode terminal, the sixth diode terminal being connected to the second circuit node.
 10. The controller of claim 1 wherein the voltage regulator includes an inverter configured to receive the second voltage signal at the first circuit node and to generate a power-on-reset signal based on at least information associated with the second voltage signal.
 11. A method for providing one or more control signals for a power system, the method comprising: receiving a first voltage signal at a first circuit node by an inverter; generating, by the inverter, a power-on-reset signal based on at least information associated with the first voltage signal; receiving a second voltage signal at a first resistor terminal of a first resistor, the first resistor further including a second resistor terminal connected to the first circuit node; receiving a third voltage signal from a second circuit node by a first transistor terminal of a first transistor, the first transistor further including a second transistor terminal connected to the first circuit node and a third transistor terminal connected to a third circuit node, the second circuit node being connected to a fourth transistor terminal of a second transistor, the second transistor further including a fifth transistor terminal and a sixth transistor terminal connected to the third circuit node; receiving, by a voltage regulator, the second voltage signal and the power-on-reset signal; converting, by the voltage regulator, the second voltage signal to a fourth voltage signal, the fourth voltage signal being smaller than the first voltage signal in magnitude; receiving, by a threshold voltage generator, the fourth voltage signal; generating, by the threshold voltage generator, a threshold voltage signal; receiving the threshold voltage signal and a fifth voltage signal from a fourth circuit node, the fourth circuit node being connected to a third resistor terminal of a second resistor and a fourth resistor terminal of a third resistor, the second resistor further including a fifth resistor terminal connected to the second circuit node, the third resistor further including a sixth resistor terminal connected to the third circuit node; determining whether the fifth voltage signal is below the threshold voltage signal in magnitude at a first time; if the fifth voltage signal is determined to be below the threshold voltage signal in magnitude at the first time, determining again whether the fifth voltage signal is below the threshold voltage signal in magnitude at a second time, the second time being later than the first time by a delay time; and if and only if the fifth voltage signal is determined to be below the threshold voltage signal in magnitude at the first time and if the fifth voltage signal is also determined to be below the threshold voltage signal in magnitude at the second time, providing an off signal as the power-on-reset signal to at least the voltage regulator.
 12. The method of claim 11 wherein the delay time is predetermined.
 13. The method of claim 11, and further comprising generating, by an oscillator, a clock signal.
 14. The method of claim 11, and further comprising: receiving the first voltage signal at a first diode terminal of a first zener diode, the first zener diode further including a second diode terminal connected to a third diode terminal of a first diode, the first diode further including a fourth diode terminal, the fourth diode terminal being connected to a fifth diode terminal of a second zener diode, the second zener diode further including a sixth diode terminal connected to the second circuit node; and receiving the first voltage signal at a seventh transistor terminal of a third transistor, the third transistor further including an eighth transistor terminal and a ninth transistor terminal, the eighth transistor terminal being connected to the first circuit node, the ninth transistor terminal being connected to the second diode terminal. 